I've been following the instructions in http://wiki.wandboard.org/index.php/External_gpios to test GPIO18 ( EIM_DA8, gpio72 ) and GPIO19 ( gpio101 ). I can change the value for GPIO19 (101), but not for GPIO18 (72)... I am using kernel 4.9.35 with WB-Quad-revB1 and I tried it in two different boards just to ensure I didn't break it. I checked my device tree, and I think I didn't assign it to anything else:

With GPIOs the things you need to check are:1. Pin muxing, did you really set the mux mode right?2. Direction is correct?3. Not blocked by any drivers? You can check this by trying to export the GPIO in sysfs ( echo 72 > /sys/class/gpio/export ) -- if you get a gpio72, it was not blocked

Tapani wrote:With GPIOs the things you need to check are:1. Pin muxing, did you really set the mux mode right?2. Direction is correct?3. Not blocked by any drivers? You can check this by trying to export the GPIO in sysfs ( echo 72 > /sys/class/gpio/export ) -- if you get a gpio72, it was not blocked